Penny Lawrence at Oxfam House in Oxford, in 2016. Lawrence, who was the U.K. charity's deputy chief executive, stepped down Monday amid a growing scandal over aid workers who paid for sex in Haiti and Chad.

Penny Lawrence at Oxfam House in Oxford, in 2016. Lawrence, who was the U.K. charity's deputy chief executive, stepped down Monday amid a growing scandal over aid workers who paid for sex in Haiti and Chad.

Haiti's president Jovenel Moise talks during a ceremony to lay the first stone for the construction of a new National Palace on the 8th anniversary of the 2010 earthquake, in Port-au-Prince, Haiti, in January.

Dieu Nalio Chery / AP

A senior Oxfam official stepped down Monday after news reports revealed that the humanitarian group had covered up evidence that some of its aid staff hired prostitutes in Chad and Haiti as the organization was delivering disaster assistance to those countries.

Penny Lawrence, Oxfam's deputy chief executive, said in a statement that she was "deeply sad" and "ashamed." She acknowledged that allegations had been known that country director for Chad, Roland van Hauwermeiren, and members of his staff, had paid for sex while they were stationed in the African country in 2006 before the team was moved to Haiti four years later.

The resignation of Lawrence came as the president of Haiti condemned the U.K.-based charity.

"Over the last few days we have become aware that concerns were raised about the behaviour of staff in Chad as well as Haiti that we failed to adequately act upon. It is now clear that these allegations - involving the use of prostitutes and which related to behaviour of both the Country Director and members of his team in Chad - were raised before he moved to Haiti," Lawrence said in the statement.

"As programme director at the time, I am ashamed that this happened on my watch and I take full responsibility," she said, adding that she was "desperately sorry for the harm and distress that this has caused to Oxfam's supporters, the wider development sector and most of all the vulnerable people who trusted us."

The scandal broke last week with a report in The London Times. It accused the charity of covering up findings from a 2011 inquiry that looked into claims that senior aid workers and the national director for Haiti paid local prostitutes for sex.

Britain's secretary for international development, Penny Mordaunt, said Sunday that the way allegations of sexual misconduct were handled by Oxfam was "shocking" and demonstrated an "absolute absence of leadership."

Mourdaunt warned Monday that Oxfam could lose more than $44 million in annual funding from her government unless it was forthcoming with full details of the scandal.

"If the moral leadership at the top of the organization isn't there, then we can't have [Oxfam] as a partner," Mordaunt told the BBC Monday ahead of a meeting with the organization's leaders.

Later, she said that Oxfam had made "a full and unqualified apology to me, and to the people of Britain and Haiti - for the appalling behaviour of some of their staff in Haiti in 2011, and for the wider failings of their organisation's response to it."

EU officials in Brussels echoed London's threat, threatening to cut more than $40 million in aid to Oxfam.

In a tweet in French, Haiti's President Jovenel Moise called charity's actions in Haiti an "extremely serious violation of human dignity."

In a separate tweet, he said there "is nothing more outrageous and dishonest than a sexual predator who uses his position as part of the humanitarian response to a natural disaster to exploit needy people in their moments of greatest vulnerability."

Haiti's Ambassador to the U.K. Bochitt Edmond tells NPR's Morning Edition that his government "is willing and getting ready to take legal action against individuals" involved in the scandal — possibly van Hauwermeiren and implicated members of his staff.

"We are very serious about it and we believe an example has to be set," he said.

Edmond called the situation "a culture of cover up."

"They knew what happened and they even said one of the reasons they did not report to the Haitian authorities is that they believed nothing would have been been done," he said. "We consider that an insult to Haiti and to the victims."

A senior Haitian government official tells the BBC that a broader investigation would be launched into foreign aid groups operating there.